In the past, various procedures for creating an opening (also referred to as an entry hole or portal) in a bone to allow inserting pins, rods, or other devices into the medullary canal required the use of drills, reamers, or curved awls. Since typical drills and reamers are essentially straight, a surgeon attempting to use one of these devices would tend to drive it off center because the patient's torso prevents access to the center of the medullary canal. In addition, the length of the drill or reamer also prevents the surgeon from sufficient maneuverability without the patient's torso interfering with drill placement. Recently, the use of curved awls has emerged as the prevalent paractice, but although their use overcomes some of the disadvantages associated with using a drill or reamer, their use still presents a difficulty in ensuring that the entry hole is correctly placed.
Determining an appropriate entry point on the surface of a bone, e.g., the femur, into which the nail can be inserted, and then executing entry at that point, is a critical step in the process of closed intramedullary nailing. In the past, surgeons have reccommended entering the femur at the tip of the greater trochanter because of particular problems which can result from attempting to enter at a more centralized location. These potential problems include: 1) damage to the femoral head blood supply, 2) femoral neck fracture, and 3) septic arthritis. Entry through the greater trochanter, however, was found to lead to eccentric reaming, which in turn caused 1) thinning, and often comminution, of the medial cortex (i.e., fracturing it into small fragments), 2) various deformations of the proximal fragment, and 3) fracture of the greater trochanter. In one study of 143 cases in which entry at the greater trochanteric was performed, femoral neck fracture occurred in 3% of the patients and comminution of the proximal fragment occurred in another 3%.
Others have proposed that the pyriformis fossa offered a more anatomically appropriate entry site because the pyriformis fossa is centered over the axis of the medullary canal. Based on radiographs and the use of an interactive graphics program, still others have recommended that the area at the junction of the femoral neck and the greater trochanter slightly anterior to or in the pyriformis fossa offers the most appropriate entry point. A study of the use of this procedure (referred to as anterior insertion of the nail), however, reported that proximal fragment comminution occurred in 26% of the cases. From the standpoint of biomechanics, a posteriorly placed entry point in the pyriformis fossa generated the least stresses in the femur. Consequently, a posteriorly placed entry portal, medial to the greater trochanter, has become the position recommended for entry position.
Since the conception of closed intramedullary fixation, various instruments as described above have been used for creating the entry hole. Recently, curved awls have emerged as the most widely used instruments in this procedure. These awls are shaped with a curved and pointed tip which is attached to a serpentine handle configured in the form of a "shepard's crook" as shown in FIG. 1. Several minor but significant problems follow from the use of a curved awl in the closed intramedullary fixation procedure.
First, as the pointed tip is inserted into the proximal femur, the tip is oriented and pushed towards the medial wall of the femur as shown in FIG. 2. If the tip is inserted too far, it will penetrate and violate the medial wall of the femur, causing an unwanted fracture of the bone. Moreover, the trochanter can fracture if the awl is inserted too aggressively.
Second, in order to centralize the entry hole for connecting it with the intramedullary canal of the bone and inserting devices, the point of the awl must be rotated laterally. This motion causes increased destruction of the internal bone structure and enlarges the entry hole. While the patient is disposed in a supine position, the interference of the handle of the awl with the patient's torso prevents the surgeon from laterally rotating the awl to centralize the tip while it is inserted in the bone as shown in FIG. 2.
Third, the cavity created by the awl is insufficiently deep to allow the alignment guide wire to be directly inserted into the medullary canal because the remaining cancellous bone structure tends to deflect the guide wire away from the central axis of the femur.
Moreover, the configuration of the presently available curved awl fails to offer the surgeon any readily ascertainable points of reference to guide her use of the device once the tip has been inserted and is no longer visible. In other words, determining whether the tip of a curved awl is being inserted in alignment with the medullary canal becomes difficult after the tip has been inserted. In addition, the configuration of the curved awl fails to provide any surface directly aligned with the point onto which a surgeon can apply pressure for positively and predictably transmitting a point force to the tip to facillitate creating an entry hole. In other words, striking or exerting force on a curved awl may result in further complications because the force may not be transmitted in alignment with the desired direction of tip travel.
It would be advantageous to provide a device for creating a entry hole in a bone during a surgical procedure (e.g. closed intramedullary fixation) that would ensure correct placement of the hole.
It would also be advantageous to provide a device which would permit a surgeon to manipulate it during use without interference from the patient's torso.
It would also be advantageous to provide a device in a configuration that would offer the surgeon using the device, points of reference for judging the position of the tip of the device with respect to the handle of the device.
It would also be advantageous to provide a device in a configuration that would allow the surgeon using it to transmit force to the tip of the device by applying pressure directly above the tip.